In processing lines where carton blanks are conveyed along a straight-line path for folding and gluing, it is relatively straightforward to engage the leading and lateral edge panels of a flat blank with plows, etc, and fold them into position for gluing. It remains a problem, however, to engage and fold the trailing panel and/or flaps of carton blanks. One solution has been to provide two processing lines at right angles to each other in what is known as an Right-Angle Gluer, a solution which is duplicative of equipment and generally wasteful of space. Another solution has been to lock the blanks onto dogs on a continuously moving chain that is calibrated to a Geneva mechanism that in turn actuates fingers which fold the trailing panels, a solution which entails considerable expense. A trailing edge folder for operating with a mechanically timed feed which employs a shaft that is intermittently rotated in conjunction with the timed carton feed is shown in U.S. Pat. No. 3,330,185.
A device for folding the trailing edges of carton blanks that has met with considerable success is described in U.S. Pat. No. 3,901,134. An endless loop having a run below the carton blank conveyer is intermittently operative and carries pivotal folding fingers that are biased to a rest position and pivoted by various cams as the finger is carried below the carton blank to engage and fold its trailing end flap. While the mechanism is adjustable to accommodate blanks of various sizes and does not require a mechanically timed feed, its speed in handling small carton blanks is limited by the speed at which successive fingers are carried onto the upper run of the loop, and smaller boxes or cartons may have to be spaced at substantial intervals from each other thereby reducing the efficiency of the apparatus. Although the speed of the fingers might be adjusted by changing the geometry of the fingers and loop, such changes are cumbersome and such apparatus is generally operated at a constant speed.
The need continues for apparatus with greater versatility for folding the trailing panels and/or flaps of carton blanks.